This invention relates to a blasting arrangement comprising a plurality of detonators, a blast control unit to which the detonators are connected and a blast key which is removably connected to the blast control unit.
A typical blasting arrangement includes a plurality of detonators and a blast control unit which is used for firing the detonators in a controlled manner. The blasting arrangement also includes a blast energy source and a blast key which constitutes a physical link in an electrical path between the blast energy source and the detonators. The blast key is usually constituted by a switch, a relay contact or a physically removable link. Once the blast key is in place and is connected to the remainder of the blast arrangement the detonators can be armed and fired. The blast key is removable—a characteristic which is intended to prevent unwanted or inadvertent firing of the detonators.
A drawback with a blast key of the aforementioned kind is that the blast key can fail, to a temporary or permanent closed state, due to a variety of sources, for example due to excessive vibration or shock. It is also possible for contacts, with which the blast key is to be engaged, to be short-circuited by any conductive material which accidentally bridges the contacts. Under this type of situation the blast control unit can cause an unplanned initiation of the detonators with potentially serious adverse consequences.